The circulating water is suffering from severe corrosion; how to solve it?
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In the circulating water tank of my workshop, the corrosion on the 20# steel plates is quite severe. The water used for replenishment comes from fresh water, some desalinated water, and the water remaining after reactions in the hydrogen production unit. The flow rate of the circulating water is 2000 NM3/H, and 50 Kg of corrosion and scale inhibitors are added daily. We only analyze the pH, Ca2+, and total phosphorus levels in the water; the current values are pH 8.6, Ca2+ 1000 ppm, and total phosphorus 1.1 mg/l. Could some expert please help determine under what conditions these values are considered acceptable? What indicators does your factory analyze, and what are the control levels for each? What are the factors that affect underscale corrosion?
The backwashing method can be used for this purpose
Are you kidding me? Backwashing? ? ? ? ? ? ? You work with filters too, right? I’m not like you; can backwashing change the components inside? You need to be honest in what you say
1. Strengthen the daily monitoring of the quality of circulating water, and take prompt corrective actions in case of any abnormalities detected； 2 Strengthen on-site management of the circulating water system to reduce the entry of debris into it ； 3 The tube sheet of the circulating water cooler can be treated with surface treatment methods such as water-cooled coatings or electroless Ni-P plating; it is essential to ensure high quality during the installation process. 4. Upgrade the material of the cooler tube bundle to stainless steel, and apply coating for corrosion protection to the tube side tube sheet or weld a stainless steel layer on it ； For circulating water quality, refer to Sinopec’s \"Regulations on Circulating Water Management\"
1. It is unknown what the concentration ratio is; salt concentration can cause corrosion. 2. The dissolved oxygen in water is saturated, making depolarizing corrosion by oxygen more likely to occur. 3. Whether the selection of corrosion and scale inhibitors is appropriate; water quality tests should be conducted before choosing such inhibitors, and targeted inhibitors should be used. 4. Conditionally, a dual-flow weakly acidic cation exchanger can be considered, which can effectively increase the concentration ratio and save water.
I think it might be that the corrosion and scale inhibition agent is not suitable. Analysis of water should be strengthened, particularly the analysis of salt content in water, so as to select appropriate corrosion and scale inhibition agents based on the water quality.
May I ask the original poster, is it the circulating water system that was put into operation after maintenance? If so, it should be considered whether there is a problem with cleaning the pre-coating. The control parameters for our plant are as follows: pH: 7.5–8 (from June to September), 7.3–7.8; total phosphorus: 8–12 ppm; turbidity ≤ 10 ppm; residual chlorine: 0.5–0.9 ppm; concentration ratio: 3–5 times. These control parameters should be related to the quality of the water.